The only constant in life is change, and that goes for your hair too. Learn how your strands transform with age, and then use our quiz and guide to get your best hair ever.

You probably have a mental picture of yourself that's been in place for years: "I'm the short brunette with the curly hair," for example. But at some point, what's actually on your head no longer matches the image you carry in your head. "Most people know that hair color changes, but not many realize that texture does too," says Heather Woolery-Lloyd, MD, a dermatologist in Miami.

"Recent research shows that individual fiber thickness, or diameter, actually increases in your early 30s before peaking and declining from the late 30s or early 40s and onward," says Pantene principal scientist Jeni Thomas, PhD. Density—the number of strands on your head--also changes. And then there's the wild card: curvature. "Studies suggest that fiber shape and curvature become more irregular with age," Dr. Thomas says. For example, a woman with uniform ringlets in her 30s may end up with half-wavy, half-kinky curls in her 60s.

To ensure your current styling strategies match the strands you have today, find your hair type and learn to make the most of it with the quiz and guide that follow.

Thick Hair: Styling Tricks

Your thick hair can probably support a style without mousse, gel, or hair spray. What you need instead are products that smooth unruliness and tame bulkiness, like smoothing creams, oils, and balms. Try Garnier Fructis Sleek & Shine Moroccan Sleek Oil Treatment ($6; drugstores), which works well on straight or wavy strands, or Intelligent Nutrients Certified Organic Styling Pomade ($29; intelligentnutrients.com), a great option for curls and textured hair.

Thick Hair: Your Best Cut

The right layering technique will help keep your hair from forming a pyramid. Stylist Eva Scrivo suggests triangular layers: "They balance thick hair's natural tendency to take on a pyramid shape by creating the opposite shape, an upside-down pyramid, or a triangle."